Honeycomb structural body and exhaust gas converting apparatus

ABSTRACT

A honeycomb structural body includes a honeycomb unit having a plurality of through holes defined by cell walls and arranged in a longitudinal direction of the honeycomb unit. The honeycomb unit includes an inorganic binder, a first zeolite, and second zeolite. The first zeolite includes at least one of a β type zeolite and a ZSM-5 type zeolite, and primary particles having an average particle diameter of approximately 0.01 μm or more and approximately 0.1 μm or less. The second zeolite includes a phosphate group zeolite and primary particles having an average particle diameter of approximately 0.5 μm or more and approximately 5 μm or less. A ratio between a mass of the first zeolite and a total mass of the first and second zeolites is approximately 0.1 or more and approximately 0.5 or less.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 toInternational Application No. PCT/JP2009/069655, filed on Nov. 19, 2009.The contents of this application are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a honeycomb structural body and anexhaust gas converting apparatus.

2. Background Art

Conventionally, as one of the automotive exhaust gas converting systems,an SCR (Selective Catalytic Reduction) system has been known in whichNOx is reduced to nitrogen and water by using ammonia.

In the SCR system, zeolite is known as a material for absorbing ammonia.

In WO06/137149A1, a honeycomb structural body including a honeycomb unitis disclosed. The honeycomb unit includes inorganic particles andinorganic fibers and/or inorganic whiskers. The inorganic particles areselected from one or more materials of a group of alumina, silica,zirconia, titania, ceria, mullite, and zeolite.

The contents of International Patent Publication No. WO06/137149A1 areincorporated herein.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a honeycomb structuralbody includes a honeycomb unit having a plurality of through holesdefined by cell walls and arranged in a longitudinal direction of thehoneycomb unit. The honeycomb unit includes an inorganic binder, a firstzeolite, and second zeolite. The first zeolite includes at least one ofa β type zeolite and a ZSM-5 type zeolite, and primary particles havingan average particle diameter of approximately 0.01 μm or more andapproximately 0.1 μm or less. The second zeolite includes a phosphategroup zeolite and primary particles having an average particle diameterof approximately 0.5 μm or more and approximately 5 μm or less. A ratiobetween a mass of the first zeolite and a total mass of the first andsecond zeolites is approximately 0.1 or more and approximately 0.5 orless.

According to another aspect of the present invention, an exhaust gasconverting apparatus includes the above-described honeycomb structuralbody.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view illustrating an example of a honeycombstructural body according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating an example of an exhaustgas converting apparatus according to an embodiment of the presentinvention;

FIG. 3 is a perspective view illustrating other modified example of thehoneycomb structural body according to an embodiment of the presentinvention; and

FIG. 4 is a perspective view illustrating the honeycomb unitconstituting the honeycomb structural body of FIG. 3.

DESCRIPTION OF EMBODIMENTS

With the conventional honeycomb structural body of WO06/137149A1, it isdesired that the NOx conversion efficiency be higher than a case wherezeolite is used as the inorganic material including a honeycomb unit.For example, phosphate group zeolite (e.g., SAPO or the like) havinghigh NOx conversion efficiency may be used as the zeolite. However,because water is absorbed by SAPO, for example, the crystal latticeconstant of SAPO changes. Therefore, the honeycomb structural bodyincluding a honeycomb unit containing SAPO has a problem of expandingand/or contracting and being easily breakable due to water absorbed toand/or desorbed from the honeycomb unit.

In light of the above-described problem of the related art, anembodiment of the present invention is capable of providing a honeycombstructural body and an exhaust gas converting apparatus that have highNOx conversion efficiency and are capable of preventing a honeycomb unitfrom being broken by absorbing and/or desorbing of water.

In the following, embodiments of the present invention are describedwith reference to the accompanying drawings.

FIG. 1 illustrates an example of a honeycomb structural body accordingto an embodiment of the present invention. The honeycomb structural body10 has an outer peripheral coating layer 12 formed on an outerperipheral surface of a single honeycomb unit 11 including pluralthrough holes 11 a partitioned by cell walls 11 b and arranged in alongitudinal direction thereof.

The honeycomb unit 11 includes a first zeolite, a second zeolite, and aninorganic binder.

The first zeolite includes a β type zeolite and/or a ZSM-5 type zeolite.

The average particle diameter of the primary particles of the firstzeolite is preferably approximately 0.01 to approximately 0.1 μm. In acase where the average particle diameter of the primary particles of thefirst zeolite is equal to or more than approximately 0.01 μm or a casewhere the average particle diameter of the primary particles of thefirst zeolite is equal to or less than approximately 0.1 μm, it isdifficult for the honeycomb unit 11 to be sufficiently prevented frombeing broken by adsorption and/or desorption of water.

The second zeolite includes a phosphate group zeolite. The phosphategroup zeolite is not limited in particular. The phosphate group zeolitemay be, for example, a SAPO (e.g., SAPO-5, SAPO-11, SAPO-34 and thelike), a MeAPO, a MeAPSO and the like. Two or more kinds of phosphategroup zeolites may be used.

The average particle diameter of the primary particles of the secondzeolite is preferably approximately 0.5 to approximately 0.5 μm. In acase where the average particle diameter of the primary particles of thesecond zeolite is equal to or more than approximately 0.5 μm, it becomesdifficult for exhaust gas to permeate through the inside of a cell wall11 b such that the first and second zeolites cannot be effectively usedfor NOx conversion. On the other hand, in a case where the averageparticle diameter of the primary particles of the second zeolite is morethan 5 μm, it is difficult for the number of pores of the honeycomb unit11 to decrease. Accordingly, it becomes easier for exhaust gas topermeate through the inside of the cell wall 11 b such that it becomeseasier for the first and second zeolites to be effectively used for NOxconversion.

The ratio of the mass of the first zeolite to the total mass of thefirst and second zeolites is preferably approximately 0.1 toapproximately 0.5. In a case where the ratio is equal to or more thanapproximately 0.1, the honeycomb unit 11 becomes fragile duringabsorption and/or desorption of water. In a case where the ratio isequal to or less than approximately 0.5, it is difficult for the NOxconversion efficiency to decrease.

With this embodiment of the present invention, it is considered that theexpanding or contracting of the honeycomb unit 11 can be reduced byproviding the first zeolite at the periphery of the second zeolite andallowing water to be adsorbed or desorbed by the second zeolite. As aresult, it becomes possible for breakage of the honeycomb structuralbody 10 to be prevented. Further, the NOx conversion rate of thehoneycomb structural body 10 becomes higher because the first zeolitealso has a NOx converting property.

Considering the NOx converting property, it is preferable for the firstzeolite to include a zeolite being ion-exchanged with Cu and/or Fe. Itis to be noted that the first zeolite may also include a zeolite whichis not ion-exchaged and/or a zeolite ion-exchanged with a metal otherthan those described above.

The first zeolite being ion-exchanged with Cu and/or Fe is preferred tohave an ion exchange amount from approximately 1.0 to approximately 5.0mass %. In a case where the ion exchange amount of the first zeolite isequal to or more than approximately 1.0 mass %, it is less likely forthe NOx conversion efficiency to become insufficient. On the other hand,in a case where the ion exchange amount of the first zeolite is equal toor less than approximately 5.0 mass %, it is difficult for the metal tobe ion-exchanged to remain as oxide and more easier to be ion-exchanged.

Considering the NOx converting property, it is preferable for the secondzeolite to include a zeolite being ion-exchanged with Cu and/or Fe. Itis to be noted that the second zeolite may also include a zeolite whichis not ion-exchaged and/or a zeolite ion-exchanged with a metal otherthan those described above.

The second zeolite being ion-exchanged with Cu and/or Fe is preferred tohave an ion exchange amount from approximately 1.0 to approximately 5.0mass %. In a case where the ion exchange amount of the second zeolite isequal to or more than approximately 1.0 mass %, it is less likely forthe NOx conversion efficiency to become insufficient. On the other hand,in a case where the ion exchange amount of the second zeolite is equalto or less than approximately 5.0 mass %, it is difficult for the metalto be ion-exchanged to remain as oxide and more easier to be positivelyion-exchanged.

Considering the NOx converting property, it is preferable for the firstzeolite to be ion-exchanged with Fe and for the second zeolite to beion-exchanged with Cu.

The honeycomb unit 11 is preferred to have a first and second zeolitecontent by weight per apparent volume from approximately 230 toapproximately 360 g/L. In a case where the first and second zeolitecontent by weight per apparent volume of the honeycomb unit 11 is equalto or more than approximately 230 g/L, there is no need for the apparentvolume of the honeycomb unit 11 to be increased in order to improve theNOx conversion efficiency. On the other hand, in a case where the firstand second zeolite content by weight per apparent volume of thehoneycomb unit 11 is equal to or less than approximately 360 g/L, it isdifficult for the strength of the honeycomb unit 11 to becomeinsufficient.

The inorganic binder(s) included in the honeycomb unit 11 is not limitedin particular. The inorganic binder(s) included in the honeycomb unit 11may be a solid content of, for example, alumina sol, silica sol, titaniasol, soluble glass, sepiolite, attapulgite, and/or boehmite. Two or morekinds of inorganic binders may be used.

The content as solid content of the inorganic binder of the honeycombunit 11 is preferably approximately 5 to approximately 30 mass %, andmore preferably approximately 10 to approximately 20 mass %. In a casewhere the content as solid content of the inorganic binder is equal toor more than 5 mass %, it is difficult for the strength of the honeycombunit 11 to decrease. On the other hand, in a case where the content assolid content of the inorganic binder is equal to or less thanapproximately 30 mass %, it becomes difficult to perform extrusionmolding of the honeycomb unit 11.

In order to increase the strength of the honeycomb unit 11, it ispreferable for the honeycomb unit 11 to further include an inorganicfiber and/or a scale-like material.

The inorganic fiber included in the honeycomb unit 11 is not limited toa particular material as long as the strength of the honeycomb unit 11can be increased. The inorganic fiber may be, for example, aluminafibers, silica fibers, silicon carbide fibers, silica alumina fibers,glass fibers, potassium titanate fibers, aluminum borate fibers and thelike. Two or more kinds of inorganic fibers may be used.

The aspect ratio of the inorganic fibers is preferably approximately 2to approximately 1000, more preferably, approximately 5 to approximately800, and still more preferably, approximately 10 to approximately 500.In a case where the aspect ratio of the inorganic fibers is equal to ormore than approximately 2, it is difficult for the effect of increasingthe strength of the honeycomb unit 11 to become low. On the other hand,in a case where the aspect ratio of the inorganic fibers is equal to orless than approximately 1000, it becomes difficult for clogging or thelike, for example, to occur in the molding die when performing extrusionmolding for forming the honeycomb unit 11. Further, it is difficult forbreakage of the inorganic fibers to occur, such that it is difficult forthe effect of increasing the strength of the honeycomb unit 11 to becomelow.

The scale-like material included in the honeycomb unit 11 is not to belimited to a particular material as long as the strength of thehoneycomb unit 11 can be increased. The scale-like material may be, forexample, glass, muscovite, alumina, silica, zinc oxide and the like. Twoor more kinds of the scale-like material may be used.

The content of the inorganic fibers and the scale-like material in thehoneycomb unit 11 is preferably approximately 3 to approximately 50 mass%, more preferably, approximately 3 to approximately 30 mass %, andstill more preferably, approximately 5 to approximately 20 mass %. In acase where the content of the inorganic fibers and the scale-likematerial is equal to or more than approximately 3 mass %, it isdifficult for the effect of increasing the strength of the honeycombunit 11 to become low. On the other hand, in a case where the content ofthe inorganic fibers and the scale-like material is equal to or lessthan approximately 50 mass %, it is difficult for the content of thefirst and second zeolite inside the honeycomb unit 11 to decrease suchthat it is difficult for the NOx conversion efficiency to become low.

The honeycomb unit 11 preferably has a porosity of approximately 25 toapproximately 40%. In a case where the porosity of the honeycomb unit 11is equal to or more than approximately 25%, it becomes easy to allowexhaust gas to permeate into the partition walls 11 b. Thus, it is easyfor the first and second zeolites to be effectively used for NOxconversion. On the other hand, in a case where the porosity of thehoneycomb unit 11 is equal to or less than approximately 40%, it becomesdifficult for the strength of the honeycomb unit 11 to be insufficient.

It is to be noted that the porosity of the honeycomb unit 11 can bemeasured by using a mercury penetration method.

The aperture ratio of a cross section of the honeycomb unit 11perpendicular to the longitudinal direction of the honeycomb unit 11 ispreferably approximately 50 to approximately 75%. In a case where theaperture ratio of the cross section perpendicular to the longitudinaldirection of the honeycomb unit 11 is equal to or more thanapproximately 50%, it becomes easy for the NOx conversion by the firstand second zeolites to be used effectively. On the other hand, in a casewhere the aperture ratio of the cross section perpendicular to thelongitudinal direction of the honeycomb unit 11 is equal to or less thanapproximately 75%, it becomes difficult for the strength of thehoneycomb unit 11 to be insufficient.

The density of the through holes 11 a of the cross section perpendicularto the longitudinal direction of the honeycomb unit 11 is preferablyapproximately 31 to approximately 124 units per cm². In a case where thedensity of the through holes 11 a of the cross section perpendicular tothe longitudinal direction of the honeycomb unit 11 is equal to or morethan approximately 31 units per cm², it becomes easy for exhaust gas andthe first and second zeolites to make contact. Thus, it becomesdifficult for the NOx conversion efficiency may decrease. On the otherhand, in a case where the density of the through holes 11 a of the crosssection perpendicular to the longitudinal direction of the honeycombunit 11 is equal to or less than approximately 124 units per cm², itbecomes difficult for the pressure loss of the honeycomb structural body10 to increase.

The thickness of the partition wall 11 b of the honeycomb unit 11 ispreferably approximately 0.10 to approximately 0.50 mm, and morepreferably approximately 0.15 to approximately 0.35 mm. In a case wherethe thickness of the partition wall 11 b is equal to or more thanapproximately 0.10 mm, it is difficult for the strength of the honeycombunit 11 to decrease. On the other hand, in a case where the thickness ofthe partition wall 11 b is equal to or less than approximately 0.50 mm,it becomes easy to allow exhaust gas to permeate into the partition wall11 b. Thus, it becomes easy for the first and second zeolites to beeffectively used for NOx conversion.

The thickness of the outer peripheral coating layer 12 is preferablyapproximately 0.1 to approximately 2 mm. In a case where the thicknessof the outer peripheral coating layer 12 is equal to or more thanapproximately 0.1 mm, it becomes difficult for the effect of increasingthe strength of the honeycomb structural body 10 to be insufficient. Onthe other hand, in a case where the thickness of the outer peripheralcoating layer 12 is equal to or less than approximately 2 mm, it becomesdifficult for the content of the first and second zeolite per volumeunit of the honeycomb structural body 10 to decrease. Thus, it becomesdifficult for the NOx conversion efficiency to decrease.

Although the shape of the honeycomb structure 10 in this embodiment issubstantially cylindrical, the shape of the honeycomb structure 10 isnot limited in particular. For example, the shape of the honeycombstructure 10 may be a substantially square pillar, a substantiallycylindroid and the like. Further, although the shape of the throughholes 11 a in this embodiment is a substantially square pillar, theshape of the through holes is not limited in particular. The shape ofthe through holes 11 a may be, for example, a substantially triangularpillar, a substantially hexagonal pillar and the like.

Next, an example of a method of manufacturing the honeycomb structuralbody 10 according to an embodiment of the present invention isdescribed. First, a raw substantially cylindrical honeycomb molded body,in which plural through holes separated by walls are formed in parallelin a longitudinal direction, is manufactured by performing extrusionmolding using a raw material paste containing a first zeolite, a secondzeolite, and an inorganic binder (and according to necessity inorganicfiber and/or scale-like material). Thereby, it becomes possible for asubstantially cylindrical honeycomb unit 11 having sufficient strengthto be obtained even if firing temperature is low.

An inorganic binder(s) included in the raw material paste is added as,alumina sol, silica sol, titania sol, soluble glass, sepiolite,attapulgite, boehmite and the like. Two or more kinds of inorganicbinders may be used.

Further, an organic binder, a dispersion medium, a molding aid, and thelike may be arbitrarily added to the raw material paste, if necessary.

The organic binder is not limited in particular. The organic binder maybe, for example, methylcellulose, carboxymethyl cellulose, hydroxylethylcellulose, polyethyleneglycole, phenol resin, epoxy resin and the like.Two or more kinds of organic binders may be used. The adding amount ofthe organic binder is preferably approximately 1 to approximately 10 wt% of the total weight of the zeolite, the inorganic binder, theinorganic fibers, and the scale-like particles.

The dispersion medium is not limited in particular. The dispersionmedium may be, for example, an organic solvent such as water andbenzene, alcohol such as methanol and the like. Two or more kinds ofdispersion media may be used.

The molding aid is not limited in particular. The molding aid may be,for example, ethylene glycol, dextrin, fatty acid, fatty acid soap,polyalcohol and the like. Two or more kinds of molding aids may be used.

When the raw material paste is prepared, it is preferable to be mixed,kneaded and the like. The raw material paste can be mixed by using amixer, an attritor (grinding mill), or the like, and can be kneaded by akneader or the like.

Next, the obtained honeycomb molded body is dried by using a dryingapparatus such as a microwave drying apparatus, a hot air dryingapparatus, a dielectric drying apparatus, a reduced pressure dryingapparatus, a vacuum drying apparatus, and a freeze drying apparatus.

Further, the obtained dried honeycomb molded body is degreased. Thedegreasing conditions are not particularly limited and can bearbitrarily selected depending on the amount and kind of organicsubstances contained in the honeycomb molded body. However, thehoneycomb molded body is preferably degreased at approximately 400° C.for approximately 2 hours.

Then, by firing the obtained degreased honeycomb molded body, thehoneycomb unit 11 having the substantially cylindrical shape isobtained. The firing temperature is preferably approximately 600 toapproximately 1200° C., and more preferably approximately 600 toapproximately 1000° C. In a case where the firing temperature is equalto or more than approximately 600° C., it becomes easy for the sinteringto progress, such that it becomes difficult for the strength of thehoneycomb unit 11 to become low. On the other hand, in a case where thefiring temperature is equal to or less than approximately 1200° C., thesintering does not excessively progress such that it becomes difficultfor the reactive sites of the first and second zeolites to decrease.

Then, an outer peripheral coating layer paste is applied onto an outerperipheral surface of the substantially cylindrical honeycomb unit 11.

The outer peripheral coating layer paste is not limited in particular.The outer peripheral coating layer paste may be, for example, a mixtureof an inorganic binder and inorganic particles, a mixture of theinorganic binder and inorganic fibers, a mixture of the inorganicbinder, the inorganic particles, and the inorganic fibers, or the like.

Further, the outer peripheral coating layer paste may further contain anorganic binder. The organic binder is not limited in particular. Theorganic binder may be, for example, polyvinyl alcohol, methylcellulose,ethylcellulose, carboxymethyl cellulose and the like. Two or more kindsof the organic binders may be used.

Then, by drying and solidifying the honeycomb unit 11 having the outerperipheral coating layer paste applied thereto, the honeycomb structuralbody 10 having the cylindrical shape is obtained. In a case where theouter peripheral coating layer paste contains an organic binder, adegreasing process is preferably performed on the honeycomb structuralbody 10. The degreasing conditions can be arbitrarily selected dependingon the amount and kind of organic substances. However, the degreasingconditions are preferably at approximately 700° C. for approximately 20minutes.

By having the honeycomb unit 11 steeped into a solution containing Cuions or Fe ions, the first and second zeolites can be ion exchanged.Further, a raw material paste containing at least one of the firstzeolite being ion exchanged by Cu and/or Fe and the second zeolite beingion exchanged by Cu and/or Fe may be used as the raw material paste.

FIG. 2 illustrates an example of an exhaust gas converting apparatus 100according to an embodiment of the present invention. In a case where aholding sealing member 20 is provided at an outer peripheral part of thehoneycomb structural body 10, an exhaust gas converting apparatus 100(see FIG. 2) is obtained by canning the honeycomb structural body 10 toa metal pipe 30. In the exhaust gas converting apparatus 100, an ejector(not illustrated) such as an ejection nozzle for ejecting ammonia or aprecursor thereof is provided at an upstream side of the honeycombstructural body 10 relative to an exhaust gas flowing direction.Thereby, ammonia is added to the exhaust gas. As a result, the NOx gasincluded in the exhaust gas is reduced by the first and second zeolitesincluded in the honeycomb unit 11. Considering preservation stability ofammonia or the precursor thereof, it is preferable to use urea water asthe precursor of ammonia. It is to be noted that ammonia is generated byheating the urea water in the exhaust gas and hydrolyzing the ureawater.

FIG. 3 illustrates another modified example of the honeycomb structuralbody 10 according to an embodiment of the present invention. Other thanthe adhesive layer 13 adhering plural honeycomb units 11′ (see FIG. 4)having plural through holes 11 a defined by cell walls 11 b and arrangedin the longitudinal direction of the honeycomb units 11′, the honeycombstructural body 10′ is the same as the honeycomb structural body 10.

The cross section of the honeycomb unit 11′ perpendicular to thelongitudinal direction of the honeycomb unit 11′ preferably has an areaof approximately 5 to approximately 50 cm². In a case where the area ofthe cross section of the honeycomb unit 11′ perpendicular to thelongitudinal direction of the honeycomb unit is equal to or more thanapproximately 5 cm², it becomes difficult for the pressure loss of thehoneycomb structural body 10′ to increase. On the other hand, in a casewhere the area of the cross section of the honeycomb unit 11′perpendicular to the longitudinal direction of the honeycomb unit isequal to or less than approximately 50 cm², it becomes difficult for thestrength against thermal stress of the honeycomb unit 11′ to beinsufficient.

The thickness of the adhesive layer 13 is preferably approximately 0.5to approximately 2 mm. In a case where the thickness of the adhesivelayer 13 is equal to or more than approximately 0.5 mm, it becomesdifficult for the adhesive strength to be insufficient. On the otherhand, in a case where the thickness of the adhesive layer is equal to orless than approximately 2 mm, it becomes difficult for the pressure lossof the honeycomb structural body 10′ to increase.

Further, except for the honeycomb units 11′ located at the outerperipheral part of the honeycomb structural body 10′ is a rectangularpillar shape, the shape of the honeycomb unit 11′ of the structural body10′ is not limited in particular. For example, the shape of thehoneycomb unit 11 may be a hexagonal pillar.

Next, an example of a method for manufacturing the honeycomb structuralbody 10′ according to an embodiment of the present invention isdescribed. First, in the same manner as the honeycomb structural body10, a honeycomb unit 11′ having a square pillar shape is formed. Then,an adhesive layer paste is applied to the outer peripheral surface ofthe honeycomb unit 11′. Then, such honeycomb units 11′ are adheredtogether and solidified by drying. Thereby, an aggregate of thehoneycomb units 11′ can be manufactured.

In this case where the aggregate of honeycomb units 11′ is manufactured,the aggregate of the honeycomb unit 11′ may be cut and polished into asubstantially cylindrical shape. Further, honeycomb units 11′, which aremolded having a substantially fan-shape or a substantially quadrateshape as the cross section perpendicular to the longitudinal directionof the honeycomb unit 11, may be adhered together to form asubstantially cylindrical-shaped aggregate of the honeycomb units 11′.

The adhesive layer paste is not to be limited in particular. Theadhesive layer paste may be, for example, a mixture of an inorganicbinder and inorganic particles, a mixture of the inorganic binder andinorganic fibers, a mixture of the inorganic binder, the inorganicparticles, and the inorganic fibers, or the like.

Further, the adhesive layer paste may further contain an organic binder.The organic binder is not limited in particular. The organic binder maybe, for example, polyvinyl alcohol, methylcellulose, ethylcellulose,carboxymethyl cellulose and the like. Two or more kinds of the organicbinders may be used.

Then, an outer peripheral coating layer paste is applied to an outerperipheral surface of the cylindrical shaped aggregate of the honeycombunits 11′. The outer peripheral coating layer paste is not limited inparticular. The outer peripheral coating layer paste may be, forexample, the same as or different from the material of the adhesivelayer paste. Further, the outer peripheral coating layer paste may havesubstantially the same composition as the adhesive layer paste.

Then, the aggregate of the honeycomb units 11 being coated with theouter peripheral coating layer paste is solidified by drying. Thereby, asubstantially cylindrical shaped honeycomb structural body 10′ isobtained. In a case where the adhesive layer paste and/or the outerperipheral coating layer paste of the honeycomb structural body 10′contains an organic binder, a degreasing process is preferably performedon the honeycomb structural body 10′. The degreasing conditions can bearbitrarily selected depending on the amount and kind of organicsubstances. However, the degreasing conditions are preferably atapproximately 700° C. for approximately 20 minutes.

It is to be noted that the honeycomb structural bodies 10 and 10′ may beformed without the outer peripheral coating layer 12.

EXAMPLES Example 1

A raw material paste 1 was prepared by mixing and kneading: a β typezeolite (930 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.05 μm; a SAPO (3100 g) used as a second zeolite beingion-exhanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 3 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Then, extrusion molding was performed on the raw material paste by usingan extruder. Thereby, a raw quadrate pillar-shaped honeycomb molded bodywas obtained. Then, the honeycomb molded body was dried for 10 minutesat 110° c. by using a microwave drying apparatus and a hot air dryingapparatus. Then, the dried honeycomb molded body is degreased at 400° c.for 5 hours. Then, the degreased honeycomb molded body is fired at 700°c. for 2 hours. Thereby, a honeycomb unit 11′ is manufactured havingquadrate pillar-shape whose single side is 34.3 mm and length is 150 mm.The honeycomb unit 11′ density of the through holes 11 a was 93units/cm² and the thickness of the cell walls was 0.23 mm.

Then, a heat resistant adhesive layer paste was prepared by mixing andkneading: alumina fiber (767 g) having an average fiber diameter of 0.5μm and an average fiber length of 15 μm; silica glass (2500 g); carboxylmethylcellulose (17 g); silica sol (600 g) of 30 mass % as solidcontent; polyvinyl alcohol (167 g); surface active agent (167 g); andalumina balloon (17 g).

16 honeycomb units 11′ were adhered together by applying the adhesivelayer paste to the honeycomb units 11. The adhesive layer paste isapplied so that the thickness of the adhesive layer is 2 mm. Theadhesive layer paste was solidified by drying at a temperature of 150°c. for 10 minutes. Then, an aggregate of the honeycomb units 11′ wasobtained by cutting the aggregate honeycomb units 11′ into a cylindricalshape with a diamond cutter so that the cross section perpendicular tothe longitudinal direction of the honeycomb units 11′ becomessubstantially point symmetrical.

Then, an adhesive layer paste was applied to the outer peripheralsurface of the aggregate of the honeycomb units 11′ so that thethickness of the outer peripheral coating layer becomes 1 mm. Then, theadhesive layer paste is solidified by drying the adhesive layer paste at150° c. for 10 minutes by using a microwave drying apparatus and a hotair drying apparatus and is degreased at 400° c. for 2 hours. Thereby, ahoneycomb structural body 10′ having a cylindrical shape with a diameterof 143.8 mm and a height of 150 mm was obtained.

Then, the honeycomb structural body 10′ was canned to a metal pipe(shell) in a state where the holding sealing member (mat made frominorganic material) 20 is provided on the outer peripheral part of thehoneycomb structural body 10′. Thereby, an exhaust gas convertingapparatus was obtained (see FIG. 2).

Example 2

A raw material paste 2 was prepared by mixing and kneading: a β typezeolite (310 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.05 μm; a SAPO (2790 g) used as a second zeolite beingion-exchanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 3 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 2 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Example 3

A raw material paste 3 was prepared by mixing and kneading: a β typezeolite (1550 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.05 μm; a SAPO (1550 g) used as a second zeolite beingion-exchanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 3 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 3 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Example 4

A raw material paste 4 was prepared by mixing and kneading: a β typezeolite (930 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.10 μm; a SAPO (2170 g) used as a second zeolite beingion-exchanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 0.5 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 4 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Example 5

A raw material paste 5 was prepared by mixing and kneading: a β typezeolite (930 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.01 μm; a SAPO (2170 g) used as a second zeolite beingion-exchanged with Cu of 2.7 mass % and including primary particleshaving an average particle diameter of 5 μm; boehmite (895 g); aluminafiber (485 g) having an average fiber diameter of 6 μm and an averagefiber length of 100 μm; methylcellulose (380 g); oleic acid (280 g); andion exchanged water (2425 g).

Except for using the raw material paste 5 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Comparative Example 1

A raw material paste 6 was prepared by mixing and kneading: a SAPO (3100g) used as a second zeolite being ion-exhanged with Cu of 2.7 mass % andhaving primary particles having an average particle diameter of 3 μm;boehmite (895 g); alumina fiber (485 g) having an average fiber diameterof 6 μm and an average fiber length of 100 μm; methylcellulose (380 g);oleic acid (280 g); and ion exchanged water (2425 g).

Except for using the raw material paste 6 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Comparative Example 2

A raw material paste 7 was prepared by mixing and kneading: a β typezeolite (1860 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.05 μm; a SAPO (1240 g) used as a second zeolite beingion-exhanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 3 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 7 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Comparative Example 3

A raw material paste 8 was prepared by mixing and kneading: a β typezeolite (930 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.15 μm; a SAPO (2170 g) used as a second zeolite beingion-exhanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 0.5 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 8 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

Comparative Example 4

A raw material paste 9 was prepared by mixing and kneading: a β typezeolite (930 g) used as a first zeolite being ion-exchanged with Fe of2.7 mass % and having primary particles having an average particlediameter of 0.01 μm; a SAPO (2170 g) used as a second zeolite beingion-exhanged with Cu of 2.7 mass % and having primary particles havingan average particle diameter of 6 μm; boehmite (895 g); alumina fiber(485 g) having an average fiber diameter of 6 μm and an average fiberlength of 100 μm; methylcellulose (380 g); oleic acid (280 g); and ionexchanged water (2425 g).

Except for using the raw material paste 9 instead of using the rawmaterial paste 1, the honeycomb structural body 10′ and the exhaust gaspurification apparatus was manufactured in the same manner as Example 1.

[Evaluation of Cracks]

Whether there are any cracks on the surface of the honeycomb unit 11′was evaluated by visual observation where the exhaust gas convertingapparatuses of the Examples 1 to 5 and the Comparative Examples 1 to 4were left to stand in the atmosphere for 2 hours.

[Measurement of NOx Conversion Efficiency]

Samples for evaluation are obtained from the honeycomb structural bodies10′ manufactured in the Examples 1 to 5 and the Comparative Examples 1to 4 by cutting out a part of the quadrate pillar shaped honeycomb unit11′ whose single side is 34.3 mm and length is 40 mm.

In a state where an imitation gas of 150° c. is allowed to flow intoeach of the samples at a space velocity (SV) of 35000/hr, a catalystevaluation apparatus SIGU (manufactured by Horiba Ltd.) was used tomeasure the outflow of nitric oxide (NO) flowing out from the samplesand to measure the NOx converting efficiency [%] expressed with aformula “(inflow of NO−outflow of NO)/(outflow of NO)×100”. Thecomposition of the imitation gas is nitric oxide (175 ppm), nitrogendioxide (175 ppm), ammonia (350 ppm), oxygen (14 volume %), carbondioxide (5 volume %), water (10 volume %), and nitrogen (balance). Theevaluation results of the cracks and the measurement results of NOxconversion efficiency are shown in Table 1.

TABLE 1 RATIO OF MASS OF NOx AVERAGE PARTICLE DIAMETER β TYPE ZEOLITE TOCONVERSION OF PRIMARY PARTICLE [μm] TOTAL MASS OF β TYPE EFFICIENCY βTYPE ZEOLITE SAPO ZEOLITE AND SAPO CRACK [%] EXAMPLE 1 0.05 3 0.3 NO 62EXAMPLE 2 0.05 3 0.1 NO 65 EXAMPLE 3 0.05 3 0.5 NO 58 EXAMPLE 4 0.10 0.50.3 NO 60 EXAMPLE 5 0.01 5 0.3 NO 58 COMPARATIVE — 3 0 YES — EXAMPLE 1COMPARATIVE 0.05 3 0.6 NO 48 EXAMPLE 2 COMPARATIVE 0.15 0.5 0.3 YES —EXAMPLE 3 COMPARATIVE 0.01 6 0.3 YES — EXAMPLE 4

According to Table 1, it can be understood that the exhaust gasconverting apparatuses of Examples 1 to 5 can prevent generation ofcracks. Further, it can be understood that the samples cut out from thehoneycomb structural bodies 10′ manufactured in Examples 1 to 5 have atendency of having high NOx conversion efficiency.

According to the above, it can be understood that by providing the firstzeolite being a β type zeolite and having primary particles having anaverage particle diameter of approximately 0.01 to approximately 0.1 μm,providing the second zeolite being a phosphate group zeolite havingprimary particles having an average particle diameter of approximately0.5 to approximately 5 μm, and providing a ratio between the mass of thefirst zeolite and the total mass of the first and second zeolites ofapproximately 0.1 to approximately 0.5, the honeycomb structural body10′ and the exhaust gas converting apparatus can have high NOxconversion efficiency and prevent the honeycomb unit 11′ from beingbroken by absorption and/or desorption of water.

Although this embodiment is described with the honeycomb structural body10′, the same effect can be attained with the honeycomb structural body10.

Further, although this embodiment is described with the β type zeolite,the same effect can be attained with a ZSM-5 zeolite.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A honeycomb structural body comprising: a honeycomb unit having aplurality of through holes defined by cell walls and arranged in alongitudinal direction of the honeycomb unit, the honeycomb unitcomprising: an inorganic binder; a first zeolite comprising: at leastone of a β type zeolite and a ZSM-5 type zeolite; and primary particleshaving an average particle diameter of approximately 0.01 μm or more andapproximately 0.1 μm or less; and a second zeolite comprising: aphosphate group zeolite; and primary particles having an averageparticle diameter of approximately 0.5 μm or more and approximately 5 μmor less, a ratio between a mass of the first zeolite and a total mass ofthe first and second zeolites being approximately 0.1 or more andapproximately 0.5 or less.
 2. The honeycomb structural body as claimedin claim 1, wherein the phosphate group zeolite comprises at least oneof SAPO, MeAPO, and MeAPSO.
 3. The honeycomb structural body as claimedin claim 2, wherein the SAPO comprises at least one of SAPO-5, SAPO-11,and SAPO-34.
 4. The honeycomb structural body as claimed in claim 1,wherein at least one of the first zeolite and the second zeolitecomprises a zeolite ion-exchanged with at least one of Cu and Fe.
 5. Thehoneycomb structural body as claimed in claim 4, wherein the firstzeolite is ion-exchanged with Fe and the second zeolite is ion-exchangedwith Cu.
 6. The honeycomb structural body as claimed in claim 5, whereinthe first zeolite being ion-exchanged with at least one of Cu and Fe hasan ion exchange amount from approximately 1.0 mass % to approximately5.0 mass %.
 7. The honeycomb structural body as claimed in claim 5,wherein the second zeolite being ion-exchanged with at least one of Cuand Fe has an ion exchange amount from approximately 1.0 mass % toapproximately 5.0 mass %.
 8. The honeycomb structural body as claimed inclaim 1, wherein the inorganic binder comprises a solid containing atleast one of alumina sol, silica sol, titania sol, soluble glass,sepiolite, attapulgite, and boehmite.
 9. The honeycomb structural bodyas claimed in claim 1, wherein the honeycomb unit further comprises atleast one of an inorganic fiber and a scale-like material.
 10. Thehoneycomb structural body as claimed in claim 9, wherein the inorganicfiber comprises at least one of alumina fiber, silica fiber, siliconcarbide fiber, silica alumina fiber, glass fiber, potassium titanatefiber, and aluminum borate fiber, and wherein the scale-like materialcomprises at least one of glass, muscovite, alumina, silica, and zincoxide.
 11. The honeycomb structural body as claimed in claim 9, whereina content of the inorganic fiber and the scale-like material isapproximately 3 mass % to approximately 50 mass %.
 12. The honeycombstructural body as claimed in claim 1, wherein the honeycomb structuralbody comprises a plurality of honeycomb units.
 13. The honeycombstructural body as claimed in claim 12, wherein a cross section of thehoneycomb units perpendicular to a longitudinal direction of thehoneycomb units has an area of approximately 5 cm² to approximately 50cm².
 14. The honeycomb structural body as claimed in claim 1, whereinthe honeycomb structural body comprises a single honeycomb unit.
 15. Thehoneycomb structural body as claimed in claim 1, comprising an outerperipheral coating layer formed on an outer peripheral surface of thehoneycomb structural body.
 16. The honeycomb structural body as claimedin claim 1, wherein the honeycomb unit has a zeolite content by weightper apparent volume from approximately 230 g/L to approximately 360 g/L.17. The honeycomb structural body as claimed in claim 1, wherein acontent of the inorganic binder as solid content is approximately 5 mass% to approximately 30 mass %.
 18. The honeycomb structural body asclaimed in claim 1, wherein the honeycomb unit has a porosity ofapproximately 25% to approximately 40%.
 19. The honeycomb structuralbody as claimed in claim 1, wherein an aperture ratio of a cross sectionof the honeycomb unit perpendicular to the longitudinal direction of thehoneycomb unit is approximately 50% to approximately 75%.
 20. Thehoneycomb structural body as claimed in claim 1, wherein a density ofthe through holes of a cross section perpendicular to the longitudinaldirection of the honeycomb unit is approximately 31 units per cm² toapproximately 124 units per cm².
 21. The honeycomb structural body asclaimed in claim 1, wherein a thickness of each of the cell walls of thehoneycomb unit is approximately 0.10 mm to approximately 0.50 mm. 22.The honeycomb structural body as claimed in claim 1, wherein thehoneycomb unit is so constructed as to be obtained by firing with atemperature of approximately 600° C. to approximately 1200° C.
 23. Thehoneycomb structural body as claimed in claim 1, wherein the honeycombstructural body is so constructed as to be used for an SCR system. 24.An exhaust gas converting apparatus comprising: the honeycomb structuralbody as claimed in claim
 1. 25. The exhaust gas converting apparatus asclaimed in claim 24, wherein the exhaust gas converting apparatus iscanned to a metal pipe in a state where a holding sealing member isprovided at an outer peripheral part of the honeycomb structural body.26. The exhaust gas converting apparatus as claimed in claim 24, whereinthe exhaust gas converting apparatus has an ejector to eject ammonia ora precursor of the ammonia provided at an upstream side of the honeycombstructural body relative to an exhaust gas flowing direction.
 27. Theexhaust gas converting apparatus as claimed in claim 26, wherein theprecursor of the ammonia comprises urea water.
 28. The exhaust gasconverting apparatus as claimed in claim 24, wherein the phosphate groupzeolite comprises at least one of SAPO, MeAPO, and MeAPSO.
 29. Theexhaust gas converting apparatus as claimed in claim 28, wherein theSAPO comprises at least one of SAPO-5, SAPO-11, and SAPO-34.
 30. Theexhaust gas converting apparatus as claimed in claim 24, wherein atleast one of the first zeolite and the second zeolite comprises azeolite ion-exchanged with at least one of Cu and Fe.
 31. The exhaustgas converting apparatus as claimed in claim 30, wherein the firstzeolite is ion-exchanged with Fe and the second zeolite is ion-exchangedwith Cu.
 32. The exhaust gas converting apparatus as claimed in claim31, wherein the first zeolite being ion-exchanged with at least one ofCu and Fe has an ion exchange amount from approximately 1.0 mass % toapproximately 5.0 mass %.
 33. The exhaust gas converting apparatus asclaimed in claim 31, wherein the second zeolite being ion-exchanged withat least one of Cu and Fe has an ion exchange amount from approximately1.0 mass % to approximately 5.0 mass %.
 34. The exhaust gas convertingapparatus as claimed in claim 24, wherein the inorganic binder comprisesa solid comprising at least one of alumina sol, silica sol, titania sol,soluble glass, sepiolite, attapulgite, and boehmite.
 35. The exhaust gasconverting apparatus as claimed in claim 24, wherein the honeycomb unitfurther comprises at least one of an inorganic fiber and a scale-likematerial.
 36. The exhaust gas converting apparatus as claimed in claim35, wherein the inorganic fiber comprises at least one of alumina fiber,silica fiber, silicon carbide fiber, silica alumina fiber, glass fiber,potassium titanate fiber, and aluminum borate fiber, and wherein thescale-like material comprise at least one of glass, muscovite, alumina,silica, and zinc oxide.
 37. The exhaust gas converting apparatus asclaimed in claim 35, wherein a content of the inorganic fiber and thescale-like material is approximately 3 mass % to approximately 50 mass%.
 38. The exhaust gas converting apparatus as claimed in claim 24,wherein the honeycomb structural body comprises a plurality of honeycombunits.
 39. The exhaust gas converting apparatus as claimed in claim 38,wherein a cross section of the honeycomb units perpendicular to alongitudinal direction of the honeycomb units has an area ofapproximately 5 cm² to approximately 50 cm².
 40. The exhaust gasconverting apparatus as claimed in claim 24, wherein the honeycombstructural body comprises a single honeycomb unit.
 41. The exhaust gasconverting apparatus as claimed in claim 24, wherein the honeycombstructural body has an outer peripheral coating layer formed on an outerperipheral surface of the honeycomb structural body.
 42. The exhaust gasconverting apparatus as claimed in claim 24, wherein the honeycomb unithas a zeolite content by weight per apparent volume from approximately230 g/L to approximately 360 g/L.
 43. The exhaust gas convertingapparatus as claimed in claim 24, wherein a content of the inorganicbinder as solid content is approximately 5 mass % to approximately 30mass %.
 44. The exhaust gas converting apparatus as claimed in claim 24,wherein the honeycomb unit has a porosity of approximately 25% toapproximately 40%.
 45. The exhaust gas converting apparatus as claimedin claim 24, wherein an aperture ratio of a cross section of thehoneycomb unit perpendicular to the longitudinal direction of thehoneycomb unit is approximately 50% to approximately 75%.
 46. Theexhaust gas converting apparatus as claimed in claim 24, wherein adensity of the through holes of the cross section perpendicular to thelongitudinal direction of the honeycomb unit is approximately 31 unitsper cm² to approximately 124 units per cm².
 47. The exhaust gasconverting apparatus as claimed in claim 24, wherein a thickness of eachof the cell walls of the honeycomb unit is approximately 0.10 mm toapproximately 0.50 mm.
 48. The exhaust gas converting apparatus asclaimed in claim 24, wherein the honeycomb unit is so constructed as tobe obtained by firing with a temperature of approximately 600° C. toapproximately 1200° C.
 49. The exhaust gas converting apparatus asclaimed in claim 1, wherein the honeycomb structural body is soconstructed as to be used for an SCR system.